U.S. Pat. No. 3,727,487 describes various means for electrically adjusting the hydraulic pressure of such a transmission system under the control of the aforementioned parameters. That patent, however, does not discuss the effect of these pressure changes upon the individual clutches and brakes acting as drive-establishing means.
U.S. Pat. No. 3,710,647, owned by the assignee of our present application, teaches the provision of a computer which emits gear-shifting commands under the control of speed sensors coacting with the input and output shafts of the transmission as well as with an engine shaft coupled with the transmission input shaft by way of a torque converter.
Even with such a computerized transmission system, however, an optimum mode of actuation of the hydraulically operated clutches and brakes is not guaranteed. Thus, the progressive engagement of the relatively rotating members of the couplers is conventionally carried out in such a way that the relative rotary speed of these members decreases substantially linearly from its maximum value at the point of cut-in to zero when the engagement is completed. This results in a large gearshift shock both at the beginning and at the end of the engagement process, accompanied by a steep initial rise of friction power. The mechanical effect of the shocks upon the components of the transmission--such as the elements of a planetary-gear train--and the heat generated by the large amount of friction are obviously undesirable phenomena.